1. Field of the Invention
The present invention relates to a fuel cell power generation system and method which generates power by causing a hydrogen rich gas produced from a raw material gas and an oxidizer gas to react with each other.
2. Related Art of the Invention
A conventional fuel cell power generation system such as one disclosed in Japanese Patent Laid-Open No. 3-257762 has a configuration shown in FIG. 10. The fuel cell power generation system shown in FIG. 10 has a reformer 41 which forms a hydrogen rich gas from a raw material gas, a burner 42 which heats the reformer 41, a nitrogen facility 46 which is connected to a line on the upstream side of the reformer 41 through nitrogen supply pipes 44 and shutoff valves 45, and a fuel cell 43 which is connected to the reformer 41 on the downstream side of the same through a reformed gas supply pipe 47, and which generates power by causing oxygen in air and generated hydrogen to react with each other. A downstream port of the fuel cell 43 on the fuel electrode 43a side is connected to the burner 42 through a hydrogen discharge connection pipe 48.
In ordinary fuel cell power generation systems, supply of a raw material gas is first stopped when the operation is stopped. When raw material gas supply is stopped, hydrogen rich gas stays in a channel comprised of the reformer 41-reformed gas supply pipe 47-fuel cell 43 fuel electrode 43a-hydrogen discharge connection pipe 48. If air flows from the burner 42 opened to atmosphere into the hydrogen rich gas channel by free convection, there is a risk of hydrogen reacting vigorously with oxygen.
When the operation is stopped, the shutoff valve 45 is opened to supply nitrogen as an inert gas to a channel comprised of the reformer 41-reformed gas supply pipe 47-fuel cell 43 fuel electrode 43a-hydrogen discharge connection pipe 48 from the nitrogen facility 46 through the nitrogen supply pipes 44 to entirely discharge hydrogen rich gas, as in this conventional fuel cell power generation system. The discharge hydrogen rich gas is burnt in the burner 42.
Thus, in the conventional fuel cell power generation system, each time the operation is stopped, the purging operation using nitrogen is performed to prevent hydrogen and air from directly reacting with each other, thus ensuring safety.
The conventional fuel cell power generation system needs to be equipped with the nitrogen facility 46 including a large nitrogen cylinder for the nitrogen-charging purging performed at every suspension of operation. For example, if the generation system is applied to an independent stationary home generator, an electric vehicle power supply or the like, a considerably large space for installation of the system is required and the initial cost for equipment is considerably high. Also, there is a need to periodically replace the nitrogen cylinder or replenish nitrogen and to take the corresponding running cost into consideration.
To solve this problem, a method not using a nitrogen cylinder may be used to discharge hydrogen rich gas staying in the channel. In such a case, however, a complicated control procedure is required and it is difficult to continuously discharge hydrogen rich gas staying in the channel in the event of an emergency, for example, a system failure. In such a situation, hydrogen rich gas stays in the channel and it is not possible to ensure sufficient level of safety from the risk of oxidization reaction of hydrogen gas.